Case Studies

Mail Relay

One of our clients came to us with a problem. They wanted to make their mail system more robust. Originally their mail system consisted of a single Microsoft Exchange server directly connected to the Internet. Because of security and performance concerns, a mail relay was added between the Exchange Server and the Internet. This server was running on the FreeBSD operating system and used Qmail as its mail transfer agent (MTA).

After about a year on this platform, our client was having problems with their primary Internet connection. They came to us with a simple request: Design a mail solution that would allow them to utilize both of their Internet connections in the even that their primary connection failed. The solution would include two mail relays, each of which would reside on its own Internet connection. Each server would be capable of failing over relay duties to the other in the event that its connection failed. The situation was further complicated by the fact that the two Internet connections were related to each other. There was no high-availability between the lines.

Our Solution

We looked at the problem and decided to stay with a free software solution. The simple fact was that the cost of such a solution was significantly less than an equivalent commercial solution from Microsoft or a Unix vendor.

We chose to go with FreeBSD for the operating system and postfix for the mail transfer agent (MTA). Postfix was written by a gentleman by the name of Wietse Venema while working at IBM. Postfix is a very fast, secure, and flexible program. Postfix had options which allowed us to perform high availability, address rewriting, and other important functions.

With the exception of a couple of out of date mail forwards, the cut-over to the new mail system went off without a hitch. The old server was blocked from receiving mail briefly, its mail queue was cleared, and then the server was replaced with the new system. Immediately the new server took over and began relaying mail. The backup server was installed shortly afterwards and high-avilability was fully tested. Months later the servers are operating flawlessly.